GB1249701A - Mechanical drive transmission - Google Patents

Abstract

1,249,701. Change-speed gear; friction clutches. CATERPILLAR TRACTOR CO. 15 Jan., 1969 [25 Jan., 1968], No. 2402/69. Headings F2C, F2D and F2L. In a motor-vehicle such as a gas-turbinepowered truck, ratio-selecting positive jaw clutches 38 &c., are power-shifted whilst input and output clutches 21, 53 are both disengaged, and a through-drive slippable friction clutch 33 is engaged to sustain torque between overall input and output shafts 18, 16 during shift. In addition a friction brake 36 is applied to the gear input shaft 18 to bring the jaw clutches to rest for synchronous shift. Clutches, brake and shift-clutches are all operated by air pressure under manual selective control only, clutch sequencing during shift being automatic. Change-speed gear.-Aligned input and output shafts 22, 51 and a parallel countershaft 68 carry meshing gear-pairs 69 ... 76, providing multiple power paths both to and from the countershaft so that the number (four, eight, sixteen or thirty-two) forward ratios is equal to 2<SP>n-1</SP> where n is the number of meshing gear pairs. Multiple reverse ratios are provided by a pair of meshing stepped wheels 78, 79 on parallel shafts, the latter wheel being meshed by an axially movable wheel 81 splined on the countershaft 68, for reverse. In the four forward, two reverse ratio gear shown in Fig 1, the gear input shaft 22 drives the countershaft 68 at either of two ratios through wheel-pairs 69, 73 or 71, 74, introduced respectively by a jaw clutch 46 clutching freelymounted wheel 73 to shaft-mounted wheel 74, or a jaw clutch 39 clutching freely mounted wheel 71 to shaft-mounted wheel 69. Two ratios from the countershaft 68 to the gear output shaft 51 are provided by wheel pairs 71, 74 and 72, 76 by clutching either wheel 71 or 72 to the output shaft 51 by a double jaw clutch 38. With the reverse idler 79 meshed with the countershaft splined wheel 81, two reverse ratios are obtained with the jaw clutch 39 engaged for countershaft drive through the wheel-pair 69, 73, idlers 78, 79 and wheel 81, and the output shaft 51 clutched at 38 to either wheel 71 or 72 to use output pair 74, 71 or 76, 72. Fig. 3, not shown, provides sixteen forward and four reverse ratios by two additional meshing wheel pairs (86, 88 and 87, 89) on the input side, with four additional jaw clutches, two (91, 93) between the two additional input wheels (86, 87) and between one (87) of them and the wheel 69, the other two (92, 94) similarly arranged on the countershaft. Clutch complex.-Constructional details of the clutches are described below. Their arrangement in the transmission is shown diagrammatically in Figs, in which, between the main input shaft 1 and gear input shaft 22 is a main friction disc clutch 21, engaged by a diaphragm spring 23 and disengaged by a piston 26 energised by compressed air, which, in compressing the diaphragm spring 23 for main clutch disengagement, also engages the through-drive seppable disc clutch 33 for directly connecting the main input shaft 18 to the final output shaft 16 through a central shaft 34 to sustain drive torque during shift. The synchronising brake 26, connects the gear input shaft 22 to the fixed casing, and is applied by separately energising a piston 35. The output or tail clutch, which connects the gear output shaft 51 to the final output shaft 16, comprises a positive jaw clutch 53, which, when disengaged during gear-shift by an air-operated piston 54, leaves the shafts 51, 16 connected by a one-way disc clutch 52 which is self-energising for forward drive. Details of these clutches appear below. Control.-A manual selector lever 32 is pivoted in one arcuate path 96, Fig. 5, past gate slots R 2 . . .R 4 corresponding to the ratios, into which the lever is moved transversely to establish a selected ratio, and provide coincidental operation of the above clutch-brake complex. Movement on the arc 96 operates through cams 98 selected combinations of pilot valves 99 ... 102 which energise, from a shift air-line 103 valves 99<SP>1</SP> . . . 102<SP>1</SP> energising differential piston motors 43 ... 83 in opposition to neutralising pressure. A complete shift sequence is as follows. Transverse movement of the manual shift lever 32 out of the notch of the ratio to be superseded releases all the pilot valves 99 &c., exhausting both sides of all the shift motors 43 &c. The same lever movement also operates a three-way pilot valve 107 which energises a valve 104 to exhaust the shift-line 103. The shift lever is then moved in the arc 96 opposite the desired gear notch, which causes cam selection of the desired combination of shift pilot valves 99 &c., and then transversely into the gear-setting notch, which causes the pilot valve 107 to deenergise the valve 104, which then pressurises the shift line 103 through a time-delay 106 (not described). The same transverse movement also causes the valve 107 to de-energise a valve 109, operating a further valve 108, which then supplies pressure air directly to the clutch sequencing line. The piston 26 of the main- and through-drive clutches 21, 33, and 54 of the tail clutch 53, are thereby operated immediately through a one-way valve 110, whilst the synchronising brake piston 35 is operated through a time-delay 113. When the shift actuators 43 &c., have become fully pressurised, shift-pressure 103 actuates the valve 108 to exhaust the clutch sequencing line, whereupon the brake piston 35 exhausts immediately through a one-way valve 112 and the clutch pistons 26, 54 exhaust through a delay 111 to re-engage the tail and main clutches, thus completing the shift sequence. Clutch construction.-The input clutch complex comprising the main clutch 21, torquesustaining through-drive slappable clutch 33 and synchronising brake 36 is detailed in Fig. 6A. The main clutch 21 comprises a disc pack 128, between the main input 18 and gear input 22, engaged by a diaphragm spring 23 through a piston 24 this clutch being released by supplying pressure air to a non-rotary piston 26 which acts on the piston 24 through a needle thrust bearing 27, pins 137 slidable axially in the inner clutchdrum 126, a friction plate 28, forming an independent drive connection between the input-driven piston 54 and the gear input shaft 22, plate 141 and springs 148. The same clutchrelease movement also engages the disc pack 143 of the through-drive clutch 33 arranged directly between the input-driven piston 24 and the central shaft 34 connected to the final output 16, compression of this clutch pack being limited only by the diaphragm spring 23 after the piston 24 contacts a limit shoulder 66 in the input member 19. The synchronising brake disc-pack 151, between the gear input shaft 22 and the casing, is engaged by separately energising the piston 35. After gear shift, on release of the brake and clutch pistons 35, 26, in that order, immediately before re-engagement of the main clutch 21, the load of the diaphragm spring 23 is carried by the through-drive clutch and the friction disc 28, which latter, which has been slipping during application of the brake 36, now applies an accelerating torque to the gear input 22 until the diaphragm spring 23 contacts an abutment 171 on the piston 24 which then transfers the spring load to the main-clutch 21, relieving the disc 28. To match the torque-capacity of the main clutch 21 to the speed requirements, lubricating oil, supplied to the clutches through passages 164, 168, accumulates, to a radial depth determined by an outlet 165, on the right face of the piston 24, where its centrifugal pressure opposes the diaphragm clutch-engaging spring 23, to provide a clutch engaging force which decreases with increase in speed. Output clutch, Fig. 6C, comprises in effect a lock-up overrunning clutch arranged between the gear output shaft 51 and final output shaft 16, the overrunning section 52 comprising a disc pack 226 having torque-responsive engaging pressure by helical splines 232 between the outer clutch drum and an input-mounted member 77, with springs 234 for initial friction drag. The positive lock-up section 53 comprises an outputsplined ring 209 having bevel faced external teeth engaging internal teeth in the inputmounted member 77, the teeth 212 being moved axially out of mesh when pressure air is applied to the annular non-rotary piston 54 to shift the ring 209 axially leftwards in opposition to a spring 217, through a needle thrust-bearing 223, plate 222 and grooved sliding pins 224. In this unlocked condition with the positive section 53 disengaged, the overrunning section 52 behaves as a one-way clutch, isolating the gear train from the output shaft 16 during gear shift.